The present invention relates to a liquid coolant feeding apparatus in a machine tool, such as a cutting machine or grinding machine, particularly to a nozzle for feeding a liquid coolant to a place of contact between a cutter or the like and a workpiece.
In a machining operation, a major factor for minimizing the machining time and machining-induced strain is to enhance contact lubrication between a cutting edge or grinding tool and a workpiece, and frictional heat dissipation or cooling. More specifically, from the viewpoint that the cutting conditions can be improved by imparting a slight amount of superficial weakening, it follows that a liquid coolant, if allowed to enter the main shearing region for cutting from all directions and adsorbed by the generated microscopic cracks or air gaps, would lower the surface energy to prevent re-adhesion. Such brittleness effect in shearing regions is very useful in that it increases the shearing angle, decreases the thickness of chips and saves the cutting force. On the other hand, since a tool will repetitively transiently form fields of plastic deformation and shearing in the surface of a workpiece, it is of the utmost importance that effective cooling and lubrication be effected for each of the transient fields of plastic deformation-and shearing which such tool contacts.
However, in conventional machine tools, a liquid coolant which is directly fed to such transient fields (tool contact regions) through a nozzle is slung by the rotation of the tool or workpiece and only superficially makes light contact with the surface of the tool and workpiece, so that it cannot be said to be contributing to effective cooling or lubrication.
In order to allow a liquid coolant in a machine tool to travel its way until it reaches the tool/workpiece contact region, where it forms a film, with satisfactory fluidity and against the centrifugal force from the rotating surface so as to successfully enter the shearing region, I have experimentally created and inspected the states of the various phases of the liquid coolant.
As a result, I have found that to amply feed a liquid coolant to a machining region, this can be achieved, not by directly injecting said liquid from a nozzle to the machining region, but by feeding it as a flow thereto. I have designed a nozzle for this object such that the nozzle, in the interior thereof, forms a liquid coolant into a group of fine turbulent flows and delivers it as a substantially cylindrical or conical veil-like waterfall around a rotating tool, with the lower end of said waterfall striking the circulatory line region on the workpiece surrounding the machining region, it being observed that the greater part of the liquid coolant reaching the circulatory line region moves as if creeping to the central portion including the rotating tool.
In the early stages of the designing of nozzles based on this finding, thinking that a waterfall-like veil of liquid coolant, which was helically rotating, surrounding the machining region struck the workpiece surface and then formed a radially inwardly directed helical flow arriving at the contact surfaces of the tool and the workpiece in the machining region and also at its vicinity, I constructed an annular nozzle adapted to discharge a liquid coolant, which was helically rotating, through a downwardly directed circumferential nozzle port, and filed this for international patent application (PCT/JP/97/00373, International Publication No. WO97/29882).
Although this nozzle construction of said 97/373 international patent application, as compared with the conventional simple nozzle construction, provides epoch-making machining speed, finish precision, and remarkable labor and energy saving, my further detailed study of the behavior of the waterfall-like veil of liquid coolant subsequent to its striking the workpiece surface has made me realize that there is room for further improvement of the feeding so method. More specifically, the lower end of the veil of liquid coolant striking the workpiece surface has a considerable portion thereof changed into an outward helical flow by centrifugal force, the remainder, which is about 50-60% of the total flow, being an inward helical flow, which forms a thickness of about 20 mm on the workpiece surface. In this case, even if the flow rate is increased using the same nozzle, the amount of the inward helical flow will remain unchanged since the centrifugal force is further increased.
Such inward helical flow, when reaching the center and striking the rotating tool, still has its large portion, though smaller than in the case of the conventional one-port nozzle, flown in all directions, during which time it is impossible to prevent chips from being somewhat caught in the tool/workpiece contact region which forms an air gap. Therefore, it can be safely assumed that if the liquid coolant is allowed, in large measure, to enter the veil from the lower end thereof, it is possible to envelop the rotating tool at the center of the thickened inward helical flow and cause the chips from the workpiece to float to the upper region in the center of the helical flow.
On the other hand, the centrifugal force of the veil of liquid coolant can be reduced by eliminating the helical rotation. Thus, if a nozzle construction, which is designed to discharge a liquid coolant downward through its circulatory nozzle port without a circumferential twist angle, is used it follows that a foreign substance clogging in the nozzle port or thereabouts would result in the liquid veil which is formed of discharged liquid coolant reaching the workpiece surface with a cut or slit formed from the clogging in the veil. (In this respect, if the liquid veil is helically rotating, the slit will disappear due to a mixable helical current in the nozzle construction or immediately below the nozzle port.) Therefore, an object of the present invention is to provide a nozzle construction designed so that even if a waterfall-like veil of discharged liquid coolant is helically rotating, the nozzle decreases the centrifugal force to ensure that the greater part of the liquid coolant reaching a workpiece""s surface is directed to the center.
To achieve the above object, the present invention provides an annular or polygonal frame-like nozzle for liquid coolant adapted to be installed above a cutter edge such as a milling tool, grinding tool or drill fixed on a vertical main shaft with said nozzle being disposed coaxially with said main shaft and being directed downward, said nozzle comprising
a) an inner peripheral wall,
b) an inner flange for an inside channel support composed of a corridor by which a liquid coolant flowing in through an inlet formed directly in said inner peripheral wall or adjacent thereto is allowed to flow substantially radially, an intermediate peripheral wall extending upward from the outer edge of said corridor to cause said radially flowing liquid to make an inward turn, and a turnaround ceiling plate having an inner peripheral edge opposed to the periphery of said inner peripheral wall so as to form an opening through which said inwardly turned flowing liquid flows out upward along said inner
peripheral wall,
c) an upper framework composed of a ceiling formed above said ceiling plate to serve as a guide surface which causes the liquid coolant flowing out upward through said opening to flow in a planar radial manner, and an outer peripheral wall serving as an outer guide surface which causes said planar radial flowing liquid to turn downward and flow downward in the periphery of said flange, said upper framework cooperating with the outer wall surface of said flange to form an outside channel, wherein the wall surface which forms said outside channel is formed at least one place therein with a recess or an uneven surface for agitating the flow,
d) a lower floor including an outer peripheral edge and an inner peripheral edge which are connected to the lower end of said outer peripheral wall positioned below the level of said inner flange, at least one difference in level located intermediate between said inner and outer peripheral edges, said lower floor forming a flow guide floor by which the liquid coolant which has reached the lower end of said outer peripheral wall is guided radially inwardly through said difference in level, wherein
e) the liquid coolant is caused to flow downward with the inner peripheral edge of said flow guide floor used as a circulatory waterfall discharging edge so as to form a waterfall-like liquid coolant veil which surrounds said cutter.
According to the above arrangement, the liquid coolant flow moves from the inside channel to the outside channel of the nozzle structure, said channels having a trap or hook construction whereby the liquid coolant flow is formed into a fine turbulent current or a particulate current, moving through the fluid guide floor and falling for discharge through the inner peripheral edge thereof (nozzle port)
In this case, the liquid coolant flow has its velocity (including rotating speed) decreased by the level difference in the fluid guide floor to have an increased thickness, so that the discharged liquid flow from the nozzle port is effectively pushed (radially inwardly) by the thick flow from behind, falling onto the workpiece surface while decreasing the veil diameter according to the flow rate, and moving mostly toward the center; thus, there is formed a central liquid layer which sufficiently covers the tool, as described above.